The present invention relates to a process for production of monoalkyl ethers of polyols, particularly monoalkyl glyceryl ethers.
Monoalkyl ethers of polyols (which may be hereinafter called as xe2x80x9cmonoalkyl ethersxe2x80x9d) represented by monoalkyl glyceryl ethers are excellent nonionic surfactants for emulsions, dispersants or detergents.
A production process of monoalkyl glyceryl ethers usually used is (1) a process which comprises synthesizing a glycidyl ether from an alcohol and an epihalohydrin such as epichlorohydrin, followed by hydrolysis. Also known are (2) a process comprising reacting an alkyl halide with glycerin by using a base, (3) a process comprising directly reacting an alcohol and glycerin in the presence of an acid catalyst, and (4) a process comprising reacting an alcohol with glycidol by using an acid or base catalyst.
In the process (1), however, selective synthesis of a glycidyl ether is difficult and in addition, there is a possibility that organic chlorides derived from the raw material may be contaminated. In the process (2), not only selective synthesis of a monoalkyl glyceryl ether is difficult, but also a large amount of salt byproducts must be treated. In addition, the process (2) involves a problem that the products are significantly colored. In the process (3), selective synthesis of a monoalkyl glyceryl ether is difficult. In addition, the process (3) is inevitably accompanied with the problem of by-production of dialkyl glyceryl ethers or dialkyl ethers resulting from an alcohol-alcohol reaction. The process (4) involves the problem that it is difficult to avoid polymerization of glycidol itself or excessive addition of glycidol to the product.
It is known that 1,7- or 2,7-alkadienyl ethers are produced by telomerization of a conjugated diene with an alcohol or polyol. In WO 93/02032 and DE 4021478 A1, there is disclosed a process for synthesizing an alkadienyl glyceryl ether by telomerization of a conjugated diene and a polyol, particularly glycerin, in a solution of a secondary alcohol such as 2-propanol. The resulting alkadienyl glyceryl ether can be then hydrogenated to give an alkyl glyceryl ether. According to this process, however, it is difficult to selectively synthesize a monoalkadienyl glyceryl ether because the alkadienyl glyceryl ethers thus produced by telomerization are changed to a mixture of the monoethers with a diether or a triether. Moreover, it is difficult to recover and reuse the catalyst in this process.
An object of the present invnetion is to provide a process for selectively producing a monoalkyl ether of a polyol, particularly a C3-6 polyol having 3 or 4 hydroxyl groups, which process is simple, advantageous from the economical viewpoint, and enables recovery and recycling of the catalyst.
The present invention provides a process for producing a monoalkyl ether, which comprises
a first step of contacting the following components (A) and (B):
(A): an aqueous liquid phase containing:
(a1) a C3-6 polyol having 3 or 4 hydroxyl groups, a palladium compound, a water-soluble tertiary phosphine or phosphite, and water; or
(a2) a C3-6 polyol having 3 to 4 hydroxyl groups, a complex of palladium and a water-soluble tertiary phosphine or phosphite, and water, and
(B): an oily liquid phase containing a conjugated diene
to give an alkadienyl ether containing an alkadienyl group resulting from dimerization of conjugated dienes; and
a second step of hydrogenating the alkadienyl group in the alkadienyl ether in a hydrogen atmosphere in the presence of a catalyst containing an element selected from the Groups 8 to 10 elements of the periodic table.
 less than First Step greater than 
Specific examples of the C3-6 polyol having 3 or 4 hydroxyl groups used in the present invention include triols such as glycerin, trimethylolmethane, trimethylolethane and trimethylolpropane, and tetraols such as pentaerythritol. Among them, triols are preferred, and glycerin is particularly preferred. In the aqueous liquid phase used in the first step, the polyol is preferably incorporated in an amount of 0.01 to 10 times, more preferably 0.1 to 10 times, especially 2 to 5 times, the weight of water.
Examples of the palladium compound contained in the aqueous liquid phase include bis(acetylacetonato)-palladium (II), palladium (II) acetate and palladium (II) chloride, of which bis(acetylacetonato)palladium (II) and palladium acetate are preferred. One or two or more of these palladium compounds may be used.
In place of using the palladium compound and water-soluble tertiary phosphine or phosphite, a complex of palladium with a water-soluble tertiary phosphine or phosphite may be used. Preferred examples of such complex include mono-, di-, tri- or higher sulfonated tetrakis(triphenylphosphine)palladium(0) and metal salts thereof. One or two or more of these palladium complexes may be used.
The palladium compound or the palladium complex with water-soluble tertiary phosphine or phosphite is preferably used in an amount of 0.0001 to 0.1 molar time, more preferably 0.001 to 0.1 molar time, especially 0.001 to 0.01 molar time of the polyol.
The water-soluble tertiary phosphine or phosphite to be incorporated, together with a palladium compound, in the aqueous liquid phase, is preferably sulfonated tertiary phosphines or phosphites, or alkali metal salts thereof. Examples thereof include mono-, di- or tri-sulfonated aliphatic (preferably of 1-20 total carbon atoms) phosphines such as trimethylphosphine, and alkali metal salts thereof; mono-, di-, tri- or higher sulfonated aromatic or aromatic-aliphatic (preferably of 8-32 total carbon atoms) phosphines such as triphenylphosphine, dimethylphenylphosphine, methyldiphenylphosphine, diethylphenylphosphine and ethyldiphenylphosphine, and alkali metal salts thereof; mono-, di-, tri-, tetra- or higher sulfonated tertiary phosphines which serve as a bidentate ligand, such as 1,2-bis(diphenylphosphino)ethane, 1,3-bis(diphenylphosphino)propane, 1,4-bis(diphenylphosphino)butane, 1,4-bis(dimethylphosphino)butane and 1,2-bis(dimethylphosphino)ethane, or alkali metal salts thereof; and sulfonated phosphites having a similar structure to the above-described sulfonated phosphines, and alkali metal salts thereof. These tertiary phosphines or phosphites act as a ligand of a part of or the whole of the palladium atoms contained in the palladium compound and can dissolve the part or whole of the palladium compound in the aqueous liquid phase. Alternatively, compounds having a carboxyl group as a substituent for a part or the whole of the sulfonic acid groups contained in the sulfonated phosphine or phosphite are also preferably used. The sulfonic acid group or carboxyl group should be contained in the tertiary phosphine or phosphite in such an amount that allows easy dissolution of the resulting tertiary phosphine or phosphite in water. Among them, preferred are sulfonated aromatic tertiary phosphines or phosphites (including the compounds serving as a bidentate ligand), and alkali metal salts thereof such as, for example, triphenylphosphine trisulfonic acid and trisodium salt thereof, and triphenylphosphine disulfonic acid and dipotassium salt thereof.
The water-soluble tertiary phosphine or phosphite is used preferably in an amount of 0.1 to 4 molar times, especially 1 to 4 molar times of the palladium compound when the tertiary phosphine or phosphite is used in a sulfonated form (or carboxylated form) or its alkali metal salt is used. A tertiary phosphine or phosphite serving as a bidentate ligand, on the other hand, is preferably used in an amount of 0.1 to 2 molar times, especially 0.5 to 2 molar times of the palladium compound.
As the conjugated diene contained in the oily liquid phase, 1,3-alkadienes and 2,4-alkadienes can be mentioned, and alkadienes of 4-6 carbon atoms, particularly 1,3-alkadienes of 4-6 carbon atoms are preferred. Specific examples thereof include 1,3-butadiene, 1,3-pentadiene, 1,3-hexadiene and isoprene. Of these, 1,3-butadiene is especially preferred. By using 1,3-butadiene, it is possible to produce monooctyl glyceryl ether and other monooctyl ethers of polyols, all of which ethers exhibit an excellent performance as a nonionic surfactant.
The monoalkyl ethers of a polyol produced according to the present invention are mono(C8-12 alkyl) ethers of a polyol corresponding to the C4-6 alkadienes used as a conjugated diene. The alkoxy group of the monoalkyl ether may be bonded to a hydroxyl group at any position of the polyol, but usually it is preferentially bonded to a primary hydroxyl group of the polyol.
As a solvent for the oily liquid phase of the present invention, it is preferred to use the conjugated diene which is also used for the reaction, but other solvents may be used, as necessary. As the other solvents, a solvent which can dissolve both the conjugated diene used in the reaction and resulting alkadienyl ethers, and is immiscible with the aqueous liquid phase is preferred. Hydrocarbon solvents and glycol diethers are preferred as the solvent.
Particularly when a polyol other than glycerin is employed, use of a glycol diether is preferred in view of control of the reaction.
Examples of the hydrocarbon solvent include C6-20 saturated aliphatic hydrocarbons such as hexane, heptane, octane, nonane, decane, undecane, dodecane, tridecane, tetradecane, pentadecane, hexadecane, heptadecane, octadecane, nonadecane and icosane. Use of the conjugated diene which is used as a reactant is also preferred as the solvent.
The glycol diethers, when used as a solvent, preferably have total carbon atoms of 20 or less. Specific preferred examples include glycol diethers such as ethyleneglycol dialkyl ethers and diethyleneglycol dialkyl ethers. Ethyleneglycol dibutyl ether, ethyleneglycol butyl methyl ether, ethyleneglycol butyl ethyl ether and diethyleneglycol dibutyl ether are more preferred.
The hydrocarbon solvent phase containing a conjugated diene may be charged at one time or introduced continuously to a reaction vessel such as autoclave. It is preferred to introduce the hydrocarbon solvent phase into the vessel in such a manner that the conjugated diene amounts to 1.0 to 10.0 molar times, especially 1.0 to 6.0 molar times of the polyol in the aqueous liquid phase.
In the first step, the reaction temperature is preferably kept at 10 to 100xc2x0 C., especially at 60 to 100xc2x0 C.
Since a larger portion of the catalyst exists in the aqueous liquid phase in the first step, it is possible to recover the aqueous liquid phase containing the catalyst and unreacted polyol in a conventional manner after the reaction, and then add thereto a necessary amount of the polyol to provide an aqueous liquid phase to be used for the reaction.
 less than Second step greater than 
The catalysts, containing an element selected from the Group 8 to 10 elements and used for hydrogenation of the alkadienyl group in the second step, include those catalysts that contain a metal selected from Fe, Co, Ni, Ru, Rh, Pd, Os, Ir and Pt, preferably a metal such as Pd, Rh, Ru, Ni or Pt that is contained in a low oxidation state. Catalysts having 1 to 10 wt. % of such metal carried on carbon, zeolite or silica alumina; Raney nickel; and oxides of such metals are preferred. The catalyst is preferably used in an amount of 0.1 to 10 wt. % based on the amount of the alkadienyl ether product. Although no particular limitation is imposed on the hydrogen pressure, a range of from normal pressure to 20 MPa is preferred.